While the theoretical possibility of light polarizing filters was known from a very early time, it was not until Alvin and Mortimer Marks grew iodine crystals in the 1940's that useful polarizing materials were first made. Polarizing materials were discovered by William Bird Herapath and were announced in the London Philosophical Papers in the mid 1860's. Cellulose had been dyed with iodine by H. Amyronn and reported in 1919 in "Accidental Double Refraction in Celluloid in 6 Cellulose" and J. Conroy in 1876 reported that microscopic crystals of iodine polarized light. Many others dyed oriented fibers prior to 1930 and reported dichroic effects.
Alvin and Mortimer Marks in the 1930's learned how to grow crystals which attached themselves in an oriented fashion to surfaces such as plastic or glass, and so produced continuous crystalline light polarizers. The new materials, for the first time, allowed the evaluation of the percentage of polarization in naturally polarized light phenomena such as glare, reflection, and the like. Several years later, Edwin Land contributed to the technology by initially using Herapath's iodo quinine sulphate as part of a plastic structure which incorporated minute crystals oriented by stretching. These new relatively inexpensive polarizing materials were almost immediately employed in a wide variety of applications, including, sunglasses, photography, scientific instrumentation, military hardware and so forth.
Of all the potential applications of the new polarizing materials, perhaps the largest promised to be the application to eyewear. Indeed, the market in polarized non-prescription sunglasses in the United States is huge. Polarized prescription glasses were first introduced as flat laminated glass blanks that were then ground to prescription. These were costly and heavy to wear because of the thickness of glass required. Despite the fact that polarized prescription lenses, especially in the beginning, were relatively expensive as compared to non-polarizing tinted lenses, the same do have a substantial but small part of the market. Nevertheless, a much larger portion of the market can use prescription polarizing glasses.
The various available alternative solutions have a number of problems. Clip-on polarizers present two extra surfaces for the collection of dust and other vision impairing matter. Clip-ons tend to be, by necessity, rather light in structure and are liable to breakage, blowing off in the wind, and other forms of instability. Accordingly, clip-on polarizers have never captured a portion of the market of prescription eyeglass wearers commensurate with the market share of polarizing non-prescription glasses as compared to tinted non-prescription glasses.
Rather, the need for light attenuating prescription sunglasses has mostly been filled by tinted non-polarizing glasses. These are made by taking finished eyeglasses (in which the lenses have been ground to the desired prescription and further ground to fit the eyeglass frame) and coating the finished product with a filter material. While this material does not exhibit polarizing characteristics, and is thus far inferior to polarizing glasses in its operating characteristics, this method does offer the advantage of a simple efficient and reliable way of attenuating light input into the eyes of the wearer.
However, a small portion of the light attenuating eyeglass market is taken by polarizing prescription sunglasses which are made by taking a glass or plastic blank of reduced thickness, adhering a polarizing film to one of its surfaces and covering the polarized film with yet another glass blank. This forms a sandwich comprising two layers of glass with a layer of polarizing material disposed therebetween. This product can also be made by injection molding of lens plastic around a polarizing filter.
It is necessary to grind the edges of the lens blank to fit them to the eyeglass frame. This can only be done after the polarizing layer has been inserted into the sandwich. This grinding is typically done in the laboratory of the eyeglass retailer. Such "labs" purchase prescription polarizing blanks with a given prescription power for grinding to the particular frame shape to be matched.
In the view of the fragile nature of the polarizing prescription lens, damage to the polarizing layer and/or the transparent sandwich members is likely to occur. The high cost of the blanks together with the above-described likelihood of damage have combined to make the polarizing sandwich lens somewhat impractical as an answer to the problem of providing polarized prescription sunglasses. Nevertheless, in the approximately fifty years since polarizing materials first became available, no other commercially viable solution has been proposed.